A well for producing hydrocarbon from subterranean earth formations is lined with tubular steel pipe and the annulus between the pipe and the well bore is filled during a completion process with a liquid cement slurry which sets and then supports the pipe in the well bore as well as filling the annulus between the pipe and the well bore. Sometimes the well, because of its depth or the formations encountered, is drilled in successive sections or lengths which have even decreasing well bore diameters. Sometimes the surface "casing" pipe is set and cemented in place in a drilled section of a well before drilling deeper. Where there is a casing pipe string cemented in place, the subsequent degree sections of the well are lined with a tubular pipe called a "liner" because the top of a liner is located in a well below the ground level. Sometimes, a string of pipe extends from a lower section of the well to the ground surface and also through a casing.
In any event, this invention is directed to a system which employs stage collars, i.e. a selectively operable valve located intermediate the length of a string of pipe. A stage valve is typically used in a cementing operation where the length of the annulus to be cemented requires a volume of cement slurry which would adversely affect the earth formations or pipe because of the pressure developed by the volume of cement slurry in a pipe or in the annulus between a pipe and a well bore. Thus, the cementing of a long length of pipe in one continuous string of pipe is accomplished by inserting a stage valve intermediate the length of the string of pipe so that a first discrete volume of cement slurry can be used to fill the annulus between the bottom of the well bore and the stage collar. While the cement slurry sets up in the lower section of pipe below the stage collar, the stage collar is opened so that mud can be circulated through the pipe, the stage valve and return to the surface via the annulus between the pipe above the stage collar and the well bore. Next, a second volume of cement slurry is injected through the pipe, the stage collar and into the upper annulus between the well bore and the pipe. When the desired amount of cement slurry has been injected into the upper annulus about the pipe, the stage collar is closed and the cement slurry sets up in the upper annulus.
The stage collar systems used to date are two in number. In the first system, the stage collar has independent, upper and lower longitudinally movable sleeve members and is normally in a closed position with ports closed by the lower sleeve member. The lower annulus below the stage valve is first cemented. Then, by dropping a closure member such as a ball, wiper plug or cementing dart at the trailing end of the flow of cement slurry for the lower annulus, the closure member will subsequently engage the lower sleeve member and close off the lower sleeve member in the stage valve. When closed off, the lower sleeve member is then moved longitudinally to an open position by hydraulic pressure generating a force acting on the closure member seated in the lower sleeve member. When the lower sleeve member is moved to an open position, fluid communication is established between the interior or bore of the pipe and the annulus between the pipe and the well bore. When the stage valve is in the open position, a second cement slurry can be introduced through the stage valve to the upper annulus between the pipe and the well bore above the stage valve. A cementing wiper plug follows the trailing end of the second cement slurry and follows the flow of cement slurry in the pipe until the plug engages and moves the upper sleeve member in the stage valve to a closed position where the opening in the stage valve to the annulus is blocked so as to retain a back pressure on the cement slurry in the annulus. Thus, the typical stage valve utilizes two independently movable sleeve members and is opened and closed by two separate closure members. In this process, the bore of the lower part of the pipe below the stage collar is not wiped free of cement and the lower zone cement may even be contaminated due to co-mingling of the cement with the buffer fluid.
In the second system, after the lower annulus is cemented, a tool with a device for operating an opening sleeve and a closing sleeve is lowered on tubing or drill pipe to first shift a sleeve valve to an open position with the opening sleeve and then shift the tubing to mechanically close the sleeve valve with the closing sleeve.
In a cementing operation, where a wiper plug follows the cementing slurry, the wiper plug has elastomer cups for wiping the bore of the pipe and the wiper plug ultimately latches into a receiving location in the string of pipe. One of the problems with the stage valve cementing system is that if a wiper plug is passed through a mechanically operated stage collar there is a change that the wiper plug will prematurely actuate the stage collar and cause a loss of pressure on the cement slurry below the stage collar. If a wiper plug is not used, then cement slurry is not cleanly removed from the lower section of pipe below a stage valve.